Hello,
The Primitives XTR series is intended to show off the unit designs that debuted during the Age of War/pre-Star League period. This series is presently slated to include four volumes of designs, and there is room for a potential fourth. The series has been delayed due to various production and quality control issues that need not be discussed openly, but will be resuming in the future, under a new schedule.
Hopefully that helps you.
Thank you,
- Herbert Beas
BattleTech
Catalyst Game Labs